The existing codes for design of highway tunnels have not had definite provisions for construction and design for single-hole and 4-lane tunnels yet. This paper, based on design angle of internal contour and, by reference to relevant research achievements, proposes, the flat ratio as a key indicator. Meanwhile in combination with the results of statistical analysis for flat ratio of internal contour of the constructed similar tunnel projects, the paper points out that a flat ratio (excluding inverted arch) of 0. 485, a flat ratio (including inverted arch)-of 0. 605 and a rise span ratio of 0. 406 in design of internal contour for separated double-hole and 8-lane or singlerhole and 4-lane tunnels show good technical economy and can provide a reference for design of 4-lane highway tunnels.%现行公路隧道设计规范对单洞4车道隧道的构造和设计尚无明确规定.基于其内轮廓设计角度,并参考相关研究成果,提出应将扁平率作为其关键指标.同时,结合对已建成类似隧道工程内轮廓扁平率的统计分析结果,指出对于分离式双洞8车道或单洞4车道隧道,其内轮廓设计时,扁平率(不合仰拱)取0.485,扁平率(含仰拱)取0.605,矢跨比取0.406,具有较好的技术经济性,可为4车道公路隧道设计提供借鉴.
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